1. Field of the Invention
The present invention relates to an energy efficient Fischer-Tropsch process. More specifically, the present invention relates to a Fischer-Tropsch process in which reaction water and other aqueous streams from a Fischer-Tropsch process are treated in a cost effective and energy efficient manner.
2. Description of the Related Art
Prior approaches degas, de-oil, and/or distill Fischer-Tropsch reaction water to partially remove dissolved and entrained contaminants. However, the resulting water product still contains lower molecular weight hydrocarbons and oxygenates. As oxygenates are known to cause corrosion, while hydrocarbons may cause foaming, the resulting water product is of little or no commercial value and requires further treatment before recovery or preparation for disposal. Thus, the water product is usually treated in expensive facilities in order to remove the contaminants. Typical treatment steps include alcohol stripping, anaerobic digestion, and biological oxidation. Such treatment steps serve to remove contaminants from the water product. Bio-treatment is costly, sensitive to operate, and generates solid wastes. Simple pH neutralization followed by offshore disposal requires regulatory variances, does not result in the recovery of any water, and requires large amounts of neutralization chemicals.
Methods for treating hydrocarbon synthesis wastewater are described in U.S. Pat. No. 3,966,633 and U.S. Patent Application 2002/0006969. Further, U.S. Pat. No. 6,225,358 discloses a method for producing heavier hydrocarbons from lighter hydrocarbons including converting synthesis gas into heavier hydrocarbons and removing contaminants from an aqueous byproduct stream. Contaminants are removed from the aqueous byproduct stream by concentrating the contaminants in a concentrator column and using the light hydrocarbons in a stripper column to remove the contaminants from the byproduct stream.
U.S. Pat. No. 6,533,945 provides a process wherein the wastewater of a hydrocarbon synthesis reactor, such as a Fischer-Tropsch reactor, is sent to a gasifier and subsequently reacted with steam and oxygen at high temperatures and pressures so as to produce synthesis gas.
Thermal oxidation, which converts harmful components to less polluting compounds, such as water vapor, carbon dioxide, and nitrogen oxides, offers the most widely proven solution to pollution from refinery, petrochemical, fine chemical, pharmaceutical, and other process industries. The use of thermal oxidizers to dispose of a wide variety of hazardous industrial wastes, especially tail gases containing a variety of sulfur compounds, is known. Descriptions of pollutant control processes can be found in Hazardous Waste Disposal by Thermal Oxidation, John Zink Company, 2001 and Thermal Oxidizers, Callidus Technologies, Inc.
What is needed is a method for treating reaction water and other aqueous streams from a Fischer-Tropsch process in an energy efficient manner with minimal adverse environmental effects and with reduced costs compared to traditional methods. Such a method would desirably allow the handling of the contaminants in an economical fashion, while even permitting the recovery of water useful for recycle to the process, as well as other uses.